1. Field of Invention
The present invention relates to semiconductor integrated circuits, and more specifically, to a low voltage reference circuit that is capable of outputting a plurality of voltages with minimal operating voltage overhead.
2. Description of Related Art
Voltage reference circuits are a critical component of many analog, digital and mixed-signal integrated circuits. Circuits such as oscillators, Phase Locked Loops (PLLs), and Dynamic Random Access Memories (DRAM) depend on stable, temperature independent voltage references. Most voltage references in use today require an operating voltage of at least 1.3 V. This is especially true for three terminal series regulated voltage references (a more desirable voltage reference due to reduced power dissipation). The output ranges of these devices vary from 1.3 V (for a bipolar process) to 1.6 V or more (for a CMOS process). As operating voltages of integrated circuits decrease with decreasing critical dimensions, the need has arisen for lower operating voltages of voltage reference circuits. At the same time, however, these reference circuits need to maintain their temperature independence. Therefore, it is desirable to provide a temperature compensated voltage reference circuit that minimizes overhead, functions at operating voltages at or below 1.3V and provides a stable reference voltage output.